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esaggese -> RE: A curious question about engine displacement (5/25/2005 12:44 AM)
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The answer to the Diesel Torque question is not that complex.
A diesel engine of the same displacement as a gas engine, with no additional boost (turbo) will not produce significantly more torque than a gas engine and it will produce MUCH less horsepower since the combustion is much slower and the engine is limited to lower RPMs.
The trick is that diesel engines are much more enegetically efficient, so you can build a larger diesel engine and have the same fuel economy as a gas engine. Thus, if you compared two engines of the same capacity, the gas engine will win in HP and torque, but if you compare two engines of the same fuel consumption (even disregarding the lower diesel fuel price), which is more relevant for anything but racing, you will have a diesel engine that´s larger and has much more torque, and probably close to the same horsepower as the gas engine.
Add to that a turbo that´s commonly attached to the diesels, and you have an engine that has plenty of torque and a decent HP.
Modern diesel engines are not very noisy, burn clean, fail very little, last forever and can compete with gas engines in HP, while consuming much less fuel.
While diesel has received lots of investment to try to make them more efficient, that´s nowhere near what the investment in research of gas engines has been. Car makers are not fools, and if they sell more gas cars than diesel cars, that´s where they'll put the money.
Finally, about the old question, what´s more important, power or HP, the answer is none. What really matters is the integral over time of the torque function. That´s close to the area below the torque curve, over the range of RPMs it will be used (obtaining the curve or torque over time is difficult and has too many variables that affect it, but the torqu curve over RPM is a good enpough approximation).
But if you have to use the HP or torque single value as a factor to decide which engine will accelerate a car in less time, the torque value will give you a more valid result. Thus, for anything other than top speed, the torque value is more important.
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